A form for a concrete tunnel lining can comprise a traveling shield following an excavating head and advanced therewith.
This form comprises an inner tunnel-lining sheathing and a form forwardly movable annular front. The inner tunnel-lining sheathing is subdivided into a plurality of independently movable sheathing member or segments with intervening segment-bridging joints. The form front positioned between the inner tunnel-lining sheathing and the traveling shield is movable forward by the pressure of the concrete which is forced into an annular space formed by the traveling shield, the surrounding earth, the inner sheathing segments and by the form front.
In the known form as taught in German Open Patent application No. 30 43 312 the inner tunnel-lining sheathing together with the form front is equipped for a complete forward motion by the pressure of the forced in concrete. That requires a comparatively high concrete pressure along with correspondingly high pressure fluctuations which impair the quality of the tunnel lining.